Electric space discharge tube system



P 1937- R. A. HEIVSING 2,093,078

ELECTRIC SPACE DISCHARGE TUBE SYSTEM Filed July 21, 1934 AAAAA AAAAAINVENTOR R. A HE/S/NG A TTORNEY Patented Sept. 14, 1937 ELECTRIC SPACEDISCHARGE TUBE SYSTEM Raymond A. Heising, Summit, N. J., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New v.York- Application July 21, 1934,Serial No. 736,282

4 Claims.

This invention relates to wave translation systems involving electricspace discharge devices,

- as for example, vacuum tube amplifiers.

An object of the invention is to simplify construction or improveoperation of such systems, and it is especially an object of theinvention to overcome deleterious efiects of inter-electrode capacitiesin such systems.

In one specific aspect the invention is a circuit using single gridvacuum tubes, which has performance characteristics like those of theusual screen grid amplifier. In this aspect,'the invention may be anamplifier of the type comprising two three-electrode vacuum tubes withthe anode of the first connected directly to the cathode of the second,and the grid of the second maintained at substantially the potential ofthe cathode of the first with respect to the waves to be amplified, andin accordance with the invention this grid may be made a shield grid,providing an electrostatic shield between the plate and the cathode ofthe second tube and making the amplifier circuit a shield grid amplifiercircuit with its two tubes having well known desirable characteristicsof the usual screen grid type of tube.

Other objects and aspects of the invention will be apparent from thefollowing description and claims:

Fig. 1 shows an amplifier of circuit configuration heretofore proposed,but with a tube which, in accordance with the invention, may besubstituted for one heretofore used in that circuit; and Fig. 2 showsthe tube which may be so substituted.

The circuit has two three-electrode vacuum tubes I and 2 amplifyingwaves from input circuit 3 and transmitting them to output circuit 4.Conductor 5 directly connects the anode of l and the cathode of 2. Theusual sources of unidirectional grid and plate potentials E0 and Eb areshown, with their preferred polarities indicatedby plus and minus signs.The plate source c0mprises a potentiometer resistance 6 shunted by aby-pass condenser 1, and has a portion shunted by a by-pass condenser 8which connects the cathode of l and the grid of 2.

Unidirectional space current from the plate source fiows in seriesthrough an inductance 9, a resistance ID, the anode-cathode space pathin tube 2, and the anode-cathode space path in tube l. Inductance 9 andresistance it present high impedance to the amplified waves.

For two tubes so connected, the efiective amplification constant ispuert=,u1(p.2+1)

and the effective output impedance is Zeff:R1(,u2+ 1) +R2 where ,ui andt2 are the amplification constants of tubes I and 2, respectively, andR1 and R2 are the plate-cathode resistances of tubes l and 2,

respectively. Using such three-electrode tubes as are normally usedwould cause the two tubes to operate as a single tube having a highamplification constant and a high internal impedance.

It is to be observed that the tube 2 has its grid l2 grounded and thevoltage is impressed between the grid and cathode by varying the po-'tential of the cathode. For variable potentials, the grid is groundedthrough a condenser. In accordance with the invention, by constructingthe tube 2 so that the grid is an effective shield between the plate andthe cathode, this amplifier circuit becomes a shield grid amplifiercircuit and the two tubes show many of the attributes of the shield gridtube. Therefore, tube 2 is shown as having the grid [2 constructed so asto also be a shield between the plate and the cathode. Any customaryform of construction may be employed. For example, usually that ofbringing the plate out at the top would be very satisfactory.

In Fig. 2 is also shown the secondarywinding of transformer l3 supplyingpower to the heater. To prevent the usual troubles caused by potentialdiiierences between the cathode and the heater, this is represented asconnected through an impedance Z which may be either high resistance orchoke coil.

This type of amplifier, two tubes in series, as stated before, operateslike a single tube. It has a high ,u. (i. e., a high efi'ectiveamplification constant) and a high output impedance like the screen gridtube. It is, therefore, primarily a voltage amplifier. It can, ofcourse, be used as a detector or for any other purpose for which ascreen grid tube would be used.

What is claimed is:

1. A wave translating system comprising an electric space dischargedevice having an anode, a cathode and a discharge control element, asecond electric space discharge device having an anode, a cathode andbut a single grid, said grid being constructed to divide the spacewithin the tube into substantially separate parts that contain thecathode and the anode respectively and adapted to form an effectiveelectrostatic shield between the anode and the cathode substantiallycompletely separating the anode and cathode electrostatically, meansconnecting the anode of the first mentioned device directly to thecathode 3 of said second device, and means for maintaining said grid atsubstantially the alternating potential of the cathode of said firstmentioned device.

2. An amplifier comprising a vacuum tube having an anode, a cathode anda grid, a second vacuum tube having an anode, a cathode and but onegrid, the latter grid being formed and positioned as a partitiondividing the space in the tube into two substantially separate partscontaining the anode and the cathoderespectively, to serve both as acontrol grid and as a shield between the anode and the cathode of saidsecond tube and substantially completely separate the anode and cathodeelectrostatically, a sourced-unidirectional voltage, means connectingsaid source and'the anode-cathode space current paths in said tubes allin serial relation, means for applying waves to be amplified betweenthe'grid and the cathode of the first mentioned tube, and'meansmaintaining said grid of said second tube substantially" at thepotential of the cathode of the first mentioned tube for said waves.

- 3.-An amplifier comprising a vacuum tube having an anode, a cathodeand a grid, a second vacuum tube'having-an anode, a cathodeand only onegrid, said latter grid being constructed as-a partition dividing thespace in the tube into substantially separate parts that respectivelycontain the cathode and the anode, and adapted to both serve as controlgrid and'give substantially complete electrostatic shielding efiectbetween theanodeand the cathode of-said second tube, said latter gridcompletely separating the anode and cathode of said second tube, meansfor applying waves to be amplified between the grid and the cathode ofthe first mentioned tube, means connectingthe anode-cathode'space pathsin said tubes in serial relation with respect to the amplified waves,and means for maintaining said grid -ofsaid second tube substantially atthe potential -oi the cathode of the first mentioned tube for I saidwaves to be amplified.

impedance for alternating -currents extending;

from the grid of said one tube to the cathode of said other tube forcooperating with said shield grid to prevent undesired feedback in saidamplifierthrough said connection.

RAYMOND A. HEISING.

